1. Technical Field
The present invention generally relates to a method for improving inversion layer mobility in a silicon carbide (SiC) metal-oxide semiconductor field-effect transistor (MOSFET). In particular, the present invention relates to forming a gate oxide on SiC substrate in the presence of metallic impurities to yield a MOSFET with improved inversion layer mobility.
2. Background Art
Silicon (Si) is, and has been, the most popular and widely used semiconductor material for the past thirty years. During this time, Si device technology has reached an advanced level because of constant refinements and improvements. The result of this constant improvement has brought silicon power devices to such levels of efficiency that they are now approaching the theoretical maximum power limit predicted for this material. This means that further refinements in device design and processing are not likely to yield substantial improvements in performance. However, this state of affairs is not acceptable for a variety of current or future applications where silicon power-devices function with heavy operating losses. To allay this situation, materials scientists have been considering various wide bandgap semiconductors as replacements for silicon.
Silicon Carbide (SiC) is an ideal semiconductor material for high voltage, high frequency and high temperature applications. This is primarily due to the large critical electric field (10 times higher than that of Si), large bandgap (3 times that of Si), large thermal conductivity (4 times that of Si), and large electron saturation velocity (twice that of Si) of SiC. These properties make SiC an ideal replacement of Si for making devices such as MOSFETs. SiC n-channel enhancement mode MOSFETs (herein referred to as SiC MOSFETs) are ideal for applications operating at high voltage, high speed and high frequency.
However, SiC MOSFETs currently fabricated by researchers have shown very poor inversion layer mobility (xcx9c1 cm2/Vs), which is one hundred times lower than the expected mobility value. This results in large power dissipation and loss of efficiency, which makes SiC MOSFETs less attractive in comparison to their Si counterparts. The lower inversion layer mobility is primarily due to the poor interface between the gate oxide and the silicon carbide substrate through which the current conduction occurs. Specifically, the interface between the gate oxide and SiC substrate has a large number of interface traps that capture the electrons which otherwise would have aided the current flow.
In view of the foregoing, a need exists for a method for improving inversion layer mobility in SiC MOSFETs. In particular, a method is needed in which an improved interface between a gate oxide layer and a silicon carbide substrate is achieved.
The present invention overcomes the drawbacks of existing SiC MOSFETs by providing a method for improving inversion layer mobility. In particular, the present invention provides a method for forming a gate oxide layer on a MOSFET such that inversion layer mobility is maximized. Generally, the method includes forming a gate oxide in the presence of metal impurities so that the oxide-substrate interface is improved.
According to a first aspect of the present invention, a method for improving inversion layer mobility in a silicon carbide metal-oxide semiconductor field-effect transistor (MOSFET) is provided. The method comprises the steps of: (1) providing a silicon carbide substrate; and (2) forming an oxide layer on a surface of the silicon carbide substrate in a presence of metallic impurities.
According to a second aspect of the present invention, a method for improving inversion layer mobility in a silicon carbide metal-oxide semiconductor field-effect transistor (MOSFET) is provided. The method comprises the steps of: (1) positioning a silicon carbide substrate and metallic impurities in a chamber; and (2) forming an oxide layer on a surface of the silicon carbide substrate by introducing nitrogen gas bubbled through deionized water into the chamber.
According to a third aspect of the present invention, a method for improving inversion layer mobility in a silicon carbide metal-oxide semiconductor field-effect transistor (MOSFET) is provided. The method comprises the steps of: (1) positioning a silicon carbide substrate and metallic impurities in a chamber; and (2) forming an oxide layer on a surface of the silicon carbide substrate by introducing a gaseous mixture of hydrogen and oxygen into the chamber.
According to a fourth aspect of the present invention, a method for improving inversion layer mobility in a silicon carbide metal-oxide semiconductor field-effect transistor (MOSFET) is provided. The method comprises the steps of: (1) providing a silicon carbide substrate and metallic impurities in a chamber heated to a temperature of approximately 1100xc2x0 C.; (2) depositing approximately 100-800 nm of a low-temperature oxide on a surface of the silicon carbide substrate; (3) introducing a gaseous mixture of hydrogen and oxygen into the chamber after the depositing step; and (4) annealing the silicon carbide substrate in argon at a temperature of approximately 950xc2x0 C.
Therefore, the present invention provides a method for improving inversion layer mobility in a MOSFET. Specifically, the present invention forms an oxide layer on a SiC substrate in the presence of metallic impurities to improve the oxide-substrate interface.